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LM3753/54 Scalable 2-Phase Synchronous Buck Controllers with Integrated FET Drivers and Linear Regulator Controller
LM3753/54
December 14, 2009
Scalable 2-Phase Synchronous Buck Controllers with Integrated FET Drivers and Linear Regulator Controller
General Description
The LM3753 and LM3754 are full featured single-output dualphase voltage-mode synchronous PWM buck controllers. They can be configured to control from 2 to 12 interleaved power stages creating a single high power output. Both controllers utilize voltage-mode control with input voltage feedforward for high noise immunity. An internal average current loop forces real time current sharing between phases during load transients.
The LM3753 supports a Tracking function, while the LM3754 supports adjustable Soft-Start. The LM3753 Tracking is always enabled, so the output is controlled both up and down. The Soft-Start function on the LM3754 can only drive the output upwards – it will not pull it down, therefore, pre-biased loads will not be discharged. Available in the 5 mm x 5 mm thermally enhanced 32-lead LLP package with a thermal pad.
Features
■ Wide input voltage range of 4.5V to 18V ■ Up to 12 channels for 300A load ■ System accuracy better than 1% ■ 0.6V to 3.6V output voltage range ■ Switching frequency from 200 kHz to 1 MHz
■ Phase current sharing ±12% max over temperature ■ Integrated 4.35V ±2.3% LDO ■ Inductor DCR or sense resistor current sensing ■ Interleaved switching for low I/O ripple current ■ Integrated synchronous NFET drivers ■ Programmable Soft-Start (LM3754) or Tracking (LM3753) ■ Pre-biased startup (LM3754) ■ Output voltage differential remote sensing ■ Minimum controllable on-time of only 50 ns ■ Programmable Enable and input UVLO ■ Power Good flag ■ OVP, UVP and hiccup over-current protection
Applications
■ CPUs, GPUs (graphic cards), ASICs, FPGAs, Large
Memory Arrays, DDR
■ High Current POL Converters ■ Networking Systems ■ Power Distribution Systems ■ Telecom/Datacom DC/DC Converters ■ Desktops, Servers and Workstations
Simplified Application
© 2009 National Semiconductor Corporation 300919
30091901
www.national.com
LM3753/54
Connection Diagram
Ordering Information
Order Number LM3753SQ LM3753SQX LM3754SQ
LM3754SQX
TRACK/SS function TRACK TRACK SS
Pre-Bias Protection SS
Pre-Bias Protection
Top View 32-Lead LLP
30091903
Package Type LLP-32 LLP-32 LLP-32
LLP-32
NSC Package Drawing SQA32A SQA32A SQA32A
SQA32A
Supplied As 1000 Units / Reel 4500 Units / Reel 1000 Units / Reel
4500 Units / Reel
www.national.com
2
LM3753/54
Pin Descriptions
Pin Number 1 2 3 4
5 6 7 8 9 10 11 12
13
14 15
16
17 18
19
20
21
22
Pin Name HG2 SW2 LG2 VDD
PGND LG1 SW1 HG1 BOOT1 PGOOD SYNCOUT SYNC
FAULT
NBASE VIN
VCC
SGND COMP
FB
VDIF
SNSM
SNSP
Description
Gate drive of the high-side N-channel MOSFET for Phase 2.
Switching node of the power stage of Phase 2.
Gate drive of the low-side N-channel MOSFETs for Phase 2.
Power supply for gate drivers. Decouple VDD to PGND with a ceramic capacitor. VDD can either be supplied by an external 5V ±10% bus, or by the internal regulator, which uses an external NPN pass device. If using the internal regulator, connect VDD to the emitter of the NPN pass device.
Power Ground. Tie PGND and SGND together on the board through the DAP.
Gate drive of the low-side N-channel MOSFETs for Phase 1.
Switching node of the power stage of Phase 1.
Gate drive of the high-side N-channel MOSFET for Phase 1.
Bootstrap of Phase 1 for the high-side gate drive power supply.
Power Good open-drain output. Active HIGH.
Synchronization Output. For multi-controller systems this pin should be connected to the SYNC pin of the next controller in daisy-chain configuration
Synchronization Input. SYNCOUT of one controller is connected to SYNC of the next controller in a daisy-chain fashion. To synchronize the whole chain of controllers to an external clock, wire the external clock to the SYNC pin of the first controller of the chain (called the Master controller). Otherwise, connect the SYNC input of the Master controller to ground and all of the controllers will be controlled by the internal oscillator of the Master.
Input/Output. Wire the FAULT pin of all controllers together. FAULT gets pulled Low during startup, an over-current fault, or an over-voltage fault. FAULT = Low signals all controllers to stop switching and prepare for the next startup sequence. The first LM3753/54 in the system (the Master) supplies the FAULT pin pull-up current for all of the controllers.
Connect to the base of external series-pass NPN if using the LM3753/54 internal LDO controller to generate VDD. Otherwise leave unconnected.
Input Voltage. Connect VIN to the input supply rail used to supply the power stages. This input is used to provide the feed-forward for the voltage control of VOUT and for generating the internal VCC voltage.
Supply for internal control circuitry. Decouple VCC to PGND with a ceramic capacitor. When VIN > 5.5V, the internal .